1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly to a technique for holding and fixing a medium and a technology for conveying a medium related to an image forming apparatus which conveys a medium by a drum conveyance method and forms an image on the medium.
2. Description of the Related Art
As a generic image forming apparatus, an inkjet recording apparatus which forms a color image on a recording medium by using color ink is known. The inkjet recording apparatus needs to cause a recording medium to make tight contact with the conveyance member which conveys the recording medium, in order to form an image in a state of close proximity between the inkjet head and the recording medium. For example, in a drum conveyance method which fixes and conveys a recording medium on the outer circumferential surface of a conveyance drum, a mode is adopted in which a recording medium is pressed using a pressing roller so as to be made tight contact with the circumferential surface of the conveyance drum, but if localized floating of the recording medium occurs due to deformation of the recording medium, or the like, wrinkles occur in the recording medium due to the pressure applied by the pressing roller. Wrinkles of this kind in the recording medium cause dramatic decline in the image quality and therefore require countermeasures.
Japanese Patent Application Publication No. 06-242703 discloses a technology for an image recording apparatus based on a pressure transfer fixing method, according to which the respective ends of recording paper in the width direction are conveyed more quickly than the central portion of the recording paper, thus preventing the occurrence of wrinkles in the recording paper, by forming an inverted crown shape in one of a pair of nip rollers in a last stage which conveys recording paper to a pressure contact section between an image carrier body and a pressure roller.
However, in the drum conveyance method described above, it is necessary to cause the paper to make tight contact along the circumferential surface of a conveyance drum, and therefore floating up in paper which has deformed stands out. In particular, when printing onto paper having a large amount of deformation, such as paper which has been printed on one surface when carrying out double-side printing, floating up of the paper is liable to occur and wrinkles are liable to arise.
Japanese Patent Application Publication No. 06-242703 discloses a shape of a pair of rollers in a nip conveyance system which conveys a recording medium to a pressure contact unit in an image recording apparatus based on a pressure transfer fixing method, but makes no concrete disclosure of a composition for fixing the recording medium in order to prevent the occurrence of wrinkles caused by deformation of the recording medium in the drum conveyance method.